Investigating Food Quality Effects on the Florida Apple Snail: Water Chemistry Effects on Periphyton Assemblages in the Northern Everglades

Transcription

1 Investigating Food Quality Effects on the Florida Apple Snail: Water Chemistry Effects on Periphyton Assemblages in the Northern Everglades Rebekah Gibble, PhD Tiffany Trent, M.S. Candidate Matthew Harwell, PhD A.R.M. Loxahatchee N.W.R. Boynton Beach, FL

2 A.R.M. Loxahatchee N.W.R. 147,000 acres Canal Levee system Water intrusion from perimeter canals to marsh interior Water chemistry gradient Vegetation alterations (McCormick et al. unpubl data see poster, GEER 2008)

3 Introduction to the Apple Snail, Pomacea paludosa Habitats and food requirements Life span and reproduction Snail kite dependence; alligators, fish, crayfish, turtles, limpkins Threats to the Apple Snail Photo by: Declining numbers since 1970s Habitat encroachment Invasive exotics Possible effects of water chemistry changes Hydrology alterations Copper, Pesticides/ Herbicides Contamination Photo by: Davesgarden.com

4 Periphyton/Water Chemistry Relations Shifts in periphyton assemblages provide early indication of water quality conditions (McCormick et al., 1996) Water chemistry determinants such as dissolved minerals, nutrients, ph are very influential on periphyton composition and abundance Algal growth and biomass accumulation of periphyton decrease with increasing distance from surrounding nutrient-rich rich canal waters. (McCormick et al., 1996) Related to lower concentrations of Tphos Nutrient rich waters will reduce algal species diversity while overall algal biomass increases (Swift and Nicholas, 1982)

5 Previous Periphyton Findings Edibility gradient of periphyton/selective grazing by snails may be present Carbon isotopic values of snails similar to green algae and diatoms (Williams and Trexler, 2006) Green algae and diatoms have higher food quality (Sklar et al., 2004) Low C:N ratios High lipid content Cyanobacteria not a good food source (Browder et al and 1994; Steinman 1996) lower lipid content, secrete unpalatable sheath, chemical defenses Cyanobacteria is now the predominant component of periphyton throughout the Refuge (Surratt et al. unpubl data see poster, GEER 2008)

6 Glass, N. H. Snail Growth (Aperture Length, Shell Length, Wet Weight) Water Quality (Total Phosphorus, Calcium, Hardness)? Browder et al., Swift and Nicholas, Sklar et al., McCormick et al. Periphyton Composition (diatom, green algae, desmids, cyanobacteria) Hypothesis: Water quality-induced changes in periphyton composition influences Florida apple snail growth/survival

7 3 Zones: Interior, Transitional, and Perimeter; 9 sites total (1 impoundment site) Lab raised juveniles (5-7 7 mm); 15 snails/mesocosm 6 replicates at each site Periphyton Supplied 8 Week exposures Exposures

8 Data Collected Snail Growth and Survival: Aperture length (mm) Shell length (mm) Wet weight (at week 0) Periphyton Samples Analyzed for: Taxonomy Nutrition Value: Protein, Carbohydrate content, ash free dry mass, C:N ratios, lipid content Apple Snails Analyzed for: Tissue analysis ash free dry mass Surface water Samples Analyzed for: Ca, SO4, Tphos Instantaneous Readings at Each Site Visit: ph Spec Conductivity DO Temp

9 Preliminary Study Results

10 Preliminary Study Results

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12 Future Water Chemistry/Apple Snail Studies Water Chemistry Control Tanks Tanks with juvenile snails housed at Refuge headquarters Water supplied from 4 sites (2, 3, 4, 9) Snails fed uniform diet of romaine lettuce Understand direct water chemistry effects on snail growth

13 Future Water Chemistry/Apple Snail Studies Egg Cluster Comparison Across Interior sites Clusters collected from Interior 8 sites and hatched at Refuge headquarters. Clusters measured for egg diameter and egg number Snail neonates measured for wet weight at birth Separate clusters analyzed for C:N ratios (reported as nutrient content, Baur and Baur, 1997). Understand relationships of snail egg clusters reproduced in varying water chemistry environments Possible advantages of larger eggs/smaller clusters (larger neonates at birth)? Clusters from Central Zone Clusters from Perimeter (West) Zone

14 Discussion Relationships between apple snail growth and periphyton composition; Correlation of periphyton composition and water gradients within the Refuge; Nutritional value of water quality-driven periphyton assemblages found along the water quality gradient within the Refuge effect ecologically significant primary consumer. Provide insight regarding causes of Pomacea paludosa declines in Refuge Supports snail kite conservation

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